ΔE 26.9, loose: different enough that you should pick on purpose. Bright Green is noticeably lighter, much more saturated, warmer than Forest Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Bright Green is noticeably lighter, much more saturated, warmer than Forest Green.
The same difference applies the other way round: Forest Green is noticeably darker, much more muted, cooler.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Forest Green on the colour wheel See Bright Green on the colour wheel
All matches: Forest Green equivalents · Bright Green equivalents